According to CDMA2000 air interfaces technical specifications, it is necessary for a base station system to transmit overhead messages to a terminal within a coverage area continuously in order to notify the terminal the latest configuration information of the system. Wherein the overhead messages bear the configuration information of the base station system, when the configuration information of the base station system changes, the configuration serial number in the overhead messages will change correspondingly, to notify terminals with changes of the configuration information of the base station system.
According to CDMA2000 protocol, after a terminal receives overhead messages transmitted from the base station system in origination state, paging response state or idle state, the terminal enters into an overhead message update sub-state. Time taken by the terminal in the overhead message update sub-state and its associated paging response state, origination response state, memory idle switch-over state or other states is directly limited by the time spent for collecting all overhead messages.
Therefore, at present, it is necessary to increase the transmission frequency of the overhead messages to reduce time spent by the terminal for collecting all overhead messages. However, the paging channel resources are limited, too much and too fast transmission of overhead messages will influence transmission of other paging messages inevitably. For example, if the transmission of common paging messages and extended channel assignment messages is influenced due to too much and too fast transmission of overhead messages, the call success ratio of the base station system and the setup time of the terminal will be affected.
Generally, within an overhead message period of 1.28 s (16 slots), it is necessary for a base station to transmit an overhead message such as System Parameters Message (SPM), Access Parameters Message (APM), CDMA Channel List Message (CCLM), Extended System Parameters Message (ESPM) and Neighbor List Message (NLM) at least once. According to different services supported by a base station system, it is also necessary for the transmitted overhead messages to include some other selectable overhead messages.
At present, the process of transmitting an overhead message according to the overhead message period is as follows: for example, for transmissions of three overhead messages OH_A, OH_B and OH_C as shown in FIG. 1, in one overhead message period, first, it is necessary to determine a slot interval for transmitting respective overhead messages, evenly distribute three overhead messages OH_A, OH_B and OH_C to be transmitted in one overhead message period. When an overhead message period starts, the base station system firstly transmit the overhead message OH_A in the first slot, then obtains the slot for transmitting the overhead message OH_B by adding the current slot for transmitting the overhead message OH_A and the determined slot interval, and transmits OH_B when the transmit slot for the overhead message OH_B arrives, and meanwhile obtains the slot for transmitting the overhead message OH_C by adding the current slot for transmitting the overhead message OH_B and the determined slot interval, and finally transmits OH_C when the transmit slot for the overhead message OH_C arrives. In this way, all overhead messages to be transmitted are transmitted in one overhead message period. When the next overhead message period starts, the base station system repeats the above process.
Although the method for transmitting an overhead message described above can meet the requirement of transmitting each overhead message at least once in one overhead message period, as it is necessary to transmit each overhead message according to the slots evenly distributed in the overhead message period, it is impossible to maximally increase the transmission frequency of overhead messages without affecting the transmission of common paging messages.